This invention relates to demineralization of liquid, whey-based material using electrodialysis.
The liquid whey remaining after the conversion of milk into cheese or casein contains a significant proportion of the nutritive materials originally present in the milk. For this reason whey is widely used as an ingredient in animal feed and human foods. The value of whey for use in foods can be enhanced by removal of some of the contained minerals. Several processes can be employed for this purpose, including ultrafiltration, ion exchange, and electrodialysis.
One important application for whey, from which the majority of minerals have been removed, is as an ingredient in infant formula. Reduced minerals whey ("RMW") has been used in premium infant formulas since the 1950's. Due to the importance of this product, and the legislation and guidelines that regulate its manufacture and sale, demineralized whey used in infant formula must meet a variety of specifications including those concerning the concentration levels of individual mineral ions.
Infant formula is one of the few human foods whose composition is mandated by law. For certain minerals, minimum levels are specified and are as important as the maximum levels. The Infant Formula Act of 1980 came into being as a result of the unfortunate situation in the late 1970's in which severe illness of a number of infants was traced to their prolonged exclusive use of a soy formula deficient in chloride.
Highly reduced minerals whey is often the majority ingredient (other than water), representing a significant portion of the total solids contained in infant formula. The overriding reason for using whey in infant formula is that it allows manufacture of a product that is similar to human milk in its (60:40) ratio of whey proteins (mainly .beta.-lactoglobulin and lactalbumin) to casein.
Electrodialysis, due to its gentle method of desalting and the composition of remaining minerals and other materials, is especially suited for producing highly demineralized whey for use in infant formula. For this end use, typically 85% to 95% of the minerals are removed from the whey in a batch operation of, for example, four to six hours duration or a continuous process with stage-by-stage recycle. However, during certain calendar periods relating to seasonal variations in milk supply, or when processing some types of whey, the electrodialysis process is at times prolonged by difficulty in removing sufficient quantities of certain divalent mineral ions, especially calcium, magnesium, and phosphate.
In milk by-products, such as whey, significant percentages of these divalent minerals are present in non-ionic form. They are bound in protein complex and do not readily enter solution as free ions, available to be removed by electrodialysis. It is due to this phenomenon that electrodialysis exhibits substantial selectivity for the relative removal of monovalent ions during the initial stages of demineralization of milk and its by-products.
Total worldwide electrodialysis production of demineralized whey is estimated at 150,000 metric tons (330 million pounds) of reduced mineral whey solids (dry basis) per year. Some electrodialysis facilities installed in dairy plants worldwide have an installed capacity to demineralize 500,000 Kg (1,100,000 pounds) or more per day of fluid whey.
Electrodialysis as a process is dependent on conductivity to create the flow of current necessary to remove mineral ions. The situation can occur near the end of extensive demineralization, (due to the combination of low conductivity, back diffusion of minerals from the salt collecting stream, and slowness of the divalent ions to release from protein complex) that the desired maximum concentration level of a particular divalent ion, usually calcium (but on occasion magnesium or phosphate) is difficult to achieve. Under these circumstances, electrodialysis is prolonged and the cost of manufacturing the product increased.
Even under usual conditions of producing highly demineralized whey by electrodialysis, the endpoint in terms of the desired level of divalent mineral ions, especially calcium, is reached considerably after the desired endpoint levels of other mineral ions such as potassium and sodium (monovalent ions). In many cases it is necessary to add back quantities of the latter minerals in order to achieve the proper composition for infant formula.
Thus, there remains a need for an improved method of demineralizing liquid, whey-based materials by electrodialysis that more efficiently achieves the desired balance of minerals required for use in infant formula and other products.